X-pop3-spooler:	POP3MAIL 2.1.0 b 4 980420 -bs-
Message-ID:	<35A52723.883F3139@astro.washington.edu>
Date:	Thu, 09 Jul 1998 20:25:07 +0000
From:	David Reiss <reiss AT astro DOT washington DOT edu>
X-Mailer:	Mozilla 4.04 [en] (X11; I; Linux 2.0.34 i586)
MIME-Version:	1.0
To:	beastium-list AT Desk DOT nl
Subject:	differences in output between c++ and pg++ compiled programs?
Sender:	Marc Lehmann <pcg AT goof DOT com>
Status:	RO
X-Status:	A
Lines:	25

Hi. I just discovered pgcc/pg++ and thought it would be great to try on
my scientific programs which usually take hours to run. I tried
compiling one program of mine (which uses lots of math routines and some
C++ classes, etc) in pg++. It compiled fine using -O6 and ran about 4x
faster than the g++ with -O2! But the numerical output is slightly
different, basically about 10% off. (Sorry I can't give more detauls w/o
explaining what the program does, which would take another 2 pages of 
typing...suffice it to say its a bunch of operations on floats and float
arrays with many do loops and reading input data files. It uses a lot of
routines from the Numerical Recipes text.)

Just to check I tested the output vs. that from g++ on a Sun Ultra. My
g++ output is exactly the same as the Sun Ultra...so my guess is there's
something interesting going on with pg++ that I don't understand.

PS. the other flags I use other than -O2 (g++) or -O6 (pg++) are:
-fhandle-exceptions -w
and I use the -m486 option with g++ on my Pentium machine.

Does anyone have any thoughts?
I dont subscribe to this list, so please email me!
thanks for any help...it would be great to get this working!

-David
reiss AT astro DOT washington DOT edu

- Raw text -